Update libraries/joomla/html/html.php

Did several things here:
* Fixed the wrong statements about the function's parameter's in the comments
* Uses ternary operator for pathonly return (wee bit less and better(?) code)
* Allow faster result if you just want the tag without looking for possible alternatives 
	-> by re-using path_only since it does not make sense asking only the path without computing
* We don't want to check the attribs if path_only is required, hence putting it in the bottom if; and made ternary operation of it
* reuse $file, 2 (potential) reasons: 1. wee bit less of code (why not?) 2. You can use this function as check for $file and changing the variable itself to the right path (if it was right or not). That way the user of the function will have a variable less (why not?)